(AP) – As Missouri prepares for its third execution in two months, a chorus of concerns is raised about the secretive process of obtaining the lethal drug.

The source of the pentobarbital used in Missouri executions remains a mystery. The Missouri Department of Corrections gets it from a compounding pharmacy but won’t reveal details, saying the secrecy is justified because the drug maker is part of the execution team.

Democratic state Rep. John Rizzo of Kansas City says he will file legislation Monday for a year-long moratorium on executions and appointment of a special commission to investigate Missouri’s process. Attorneys for death row inmates have asked U.S. attorneys to intervene. Even a federal appeals judge has expressed outrage.

A Corrections Department spokesman says the procurement process complies with all laws.